1. Field of the Invention
The present invention relates generally to a Personal Digital Assistant (PDA) telephone having functions of a PDA and a mobile telephone. In particular, the present invention relates to a method for checking the voltage of the PDA telephone when both the PDA and the telephone are in their OFF states.
2. Description of the Related Art
In a PDA telephone having functions of a PDA and a mobile telephone, since the PDA is the main application, the telephone cannot be used at low voltages (such as, 3.6V), thereby preventing user data stored in a random access memory (RAM) of the PDA from being eliminated due to a voltage drop caused by the mobile telephone. Particularly, in a Global System for Mobile communications (GSM) telephone, a voltage drop that occurs after call connection is significant. The user data stored in a synchronous dynamic RAM (SDRAM) of the PDA must be protected if the telephone function is to be used in low voltage situations.
In the PDA telephone, when both the PDA and the telephone are in their ON states, a controller of the PDA checks the voltage of the PDA telephone. When the voltage of the PDA telephone goes to 3.8V, the controller of the PDA senses a low-battery condition. When the voltage of the PDA telephone goes to 3.6V, the controller of the PDA turns off the telephone. Thereafter, when the voltage of the PDA telephone goes to 3.5V, the controller of the PDA senses a very low-battery condition. When the voltage of the PDA telephone goes to 3.4V, the controller of the PDA turns off the PDA by switching the PDA into a sleep mode. In the sleep mode, user data stored in the RAM of the PDA is automatically refreshed, thereby preventing the user data from being eliminated. In the sleep mode, only the automatic refresh function is enabled, and the PDA functions cannot work. If a user of the PDA telephone inputs a power-on key while both the telephone and the PDA are in their OFF states, the telephone and the PDA enter the ON states. When the PDA is turned off or enters the sleep mode, the controller of the PDA is internally awakened to control the user data stored in the RAM of the PDA to be automatically refreshed, but cannot check the voltage of the PDA telephone any longer. Therefore, after the PDA is turned off, the voltage of the PDA telephone is checked by a second low voltage sensor and the PDA telephone is supplied with a voltage from a secondary chemical battery instead of its main power supply. Once the voltage of the PDA telephone goes to 2.9V, the second low voltage sensor senses a low-battery condition and informs the internally-awakened controller of the PDA of the low-battery condition. Then the controller of the PDA switches the PDA telephone into a battery default mode. At this time, if the user of the PDA telephone inputs a power-on key, the PDA telephone is momentarily turned on and then immediately turned off, thereby preventing the user from using the PDA telephone.
Also, when the PDA is in the ON state and the telephone is in the OFF state, the controller of the PDA checks the voltage of the PDA telephone. When the voltage of the PDA telephone goes to 3.8V, the controller of the PDA senses a low-battery condition. When the voltage of the PDA telephone goes to 3.5V, the controller of the PDA senses a very low-battery condition. When the voltage of the PDA telephone goes to 3.4V, the controller of the PDA turns off the PDA or switches the PDA into the sleep mode. If the user of the PDA telephone inputs a power-on key while both the telephone and the PDA are in the OFF states, the telephone and the PDA enter the ON state. When the PDA is turned offor enters the sleep mode, the controller of the PDA is internally awakened to control user data stored in the RAM of the PDA to be automatically refreshed, but cannot check the voltage of the PDA telephone any longer. Thus, after the PDA is turned off, the voltage of the PDA telephone is checked by the second low voltage sensor and the PDA telephone is supplied with a voltage from the secondary chemical battery instead of its main power supply. Once the voltage of the PDA telephone goes to 2.9V, the second low voltage sensor senses a low-battery condition and informs the internally-signaled controller of the PDA of the low-battery condition. Then the controller of the PDA switches the PDA telephone into a battery default mode. At this time, if the user of the PDA telephone inputs a power-on key, the PDA telephone is momentarily turned on and then immediately turned off, thereby preventing the user from using the PDA telephone.
Also, when the PDA is in the OFF state and the telephone is in the ON state, a controller of the telephone checks the voltage of the PDA telephone. At this time, the PDA is in the OFF state or in the sleep mode, and the internally-awakened controller of the PDA controls user data stored in the RAM of the PDA to be automatically refreshed. When the voltage of the PDA telephone goes to 3.64V, the controller of the telephone awakes the controller of the PDA and generates an alarm that informs the user of the PDA telephone that the voltage of the PDA telephone is low and should be recharged. Thereafter, once the voltage of the PDA telephone goes to 3.6V, the controller of the telephone turns off the telephone. From this time on, the second low voltage sensor checks the voltage of the PDA telephone, and the PDA telephone is supplied with a voltage from the secondary chemical battery instead of the main power supply. When the voltage of the PDA telephone goes to 2.9V, the second low voltage sensor senses a low-battery condition and informs the internally-awakened controller of the PDA of the low-battery condition. Then the controller of the PDA switches the PDA telephone into a battery default mode. At this time, if the user of the PDA telephone inputs a power-on key, the PDA telephone is momentarily turned on and then immediately turned off, thereby preventing the user from using the PDA telephone.
However, when both of the PDA and the telephone are in the OFF states, there is no way to check the voltage of the PDA telephone. In other words, if the user leaves the PDA telephone as it is in a specific situation, the PDA and the telephone are naturally discharged and enter their OFF states. Thereafter, when the user turns on the PDA telephone to use the PDA telephone, the telephone booted by the PDA telephone tries to search for a base station, resulting in a significant voltage drop. Thus, the controller of the PDA naturally generates a hardware reset, resulting in a situation where the user data stored in the SDRAM may be eliminated.